The present invention relates generally to printers and more particularly to a ribbon fold out mechanism mounted in the lid of a thermal printer to facilitate loading of ribbon media and printhead maintenance.
The invention relates to clutch assemblies, in particular, to clutch assemblies for printers.
A thermal printer is usually provided with a printhead which comprises a large number of exothermic resistors arranged on an electrically insulating base. By selectively applying electric current to the exothermic resistors, heat is generated and applied to a thermo-sensitive print medium so as to print characters, pictures or both. The basic construction of a conventional thermal transfer printer includes a platen, thermal printhead, ribbon supply and take up mechanism, stepping motor and a gear train for driving the platen. A continuous strip of print media (e.g., paper, cloth, etc.) usually from a clamped print media roll is positioned between the platen and the ribbon with the thermal printhead caused to press the ribbon against the print media thereby printing characters or pictures on the print media strip using heat generated from the thermal printhead.
One of the most important aspects for the user in setting up a thermal transfer printer for printing is ribbon and media loading. Ribbon loading in conventional thermal transfer printers is a complicated, generally undesirable task, which frequently involves ten or more steps. The usual steps are unlatching the printer, opening the lid of the printer, loading the ribbon supply roll, loading the ribbon take up roll, opening up the ribbon mechanism, threading the ribbon, wrapping the ribbon around the ribbon mechanism, taping it to the ribbon take up roll, taking up the ribbon slack, closing the lid of the printer and finally, re-latching the printer. Of the above-described steps, ribbon threading is usually the most difficult step to accomplish and as such can be a source of frustration for the user. Media loading usually requires the user to thread the media under or through the ribbon mechanism. Furthermore, conventional thermal transfer printers do not provide easy access to the thermal printhead for maintenance, which adds to the overall cost of meeting the printing needs of the average user.
Therefore, the need arises for an improved, low cost thermal transfer printer, which significantly reduces the number of steps involved in ribbon and media loading. Such a printer should preferably be capable of loading ribbon and media without having to thread through/around the ribbon mechanism. The need also arises for a thermal transfer printer, which provides easier access to the thermal printhead for regular maintenance by the user.
In the past, printer clutch assemblies have typically used a felt or felt-like material or metal on the interface of clutch disks to provide the necessary frictional coupling. In the past, it has been found that injection molding of a plastic did not result in a smooth, even surface. Therefore, trying to produce injection molded clutch disk pairs did not result in a viable clutch assembly, since the actual point or points of contact between the two disks was minimal. There tended to be approximately three high points on a disk. An injection molded plastic clutch assembly would be highly desirable, if one were able to mold an acceptable disk with the desired mechanical properties. It would help achieve lower costs and smaller sizes in items of which it is a component, if the materials chosen for the clutch disks not only have the desirable coefficients of friction, but also have good wear characteristics against each other.
The present invention meets the above needs and is directed to a printer comprising a base having a platen, a lid coupled to the base, the lid having an open position and a closed position, a ribbon mechanism coupled to the lid, means for driving the ribbon mechanism and the platen when the lid is in the closed position and means for automatically presenting the ribbon mechanism for loading of ribbon when the lid is in the open position.
The invention comprises a clutch disk made of plastic, which may be used in a printer mechanism. The design utilizes two different injection molded plastic clutch disks that run face to face to produce relatively high dynamic frictional forces and relatively low static frictional forces. The two plastics used are LNP Engineering Plastics DFL-4036 and RCL-4036. The clutch assembly uses raised areas on one of the pair of clutch disks. The raised areas allow a better overall contact between the disks so as to achieve a higher effective dynamic coefficient of friction and a lower effective static coefficient of friction. Samples of various designs of the raised areas are arranged so that spaces exist between the sectors of raised areas. These spaces allow for debris to be swept into these non-contacting areas so as to reduce wear from particles tending to be trapped between the contacting surfaces of the clutch disks. The materials chosen for the clutch disks not only have the desirable coefficients of friction, but also wear well against each other.